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Product and Quotient Rule!!!

There's a question which confuses me because of its wording.

Given that u=(1+x)/(1-x) , find du/dx.

I can do that part, but then the following wording confuses me:

using this result, and the chain rule, show that if y=((1+x)/(1-x))^3 , dy/dx = (6(1+x)^2)/((1-x)^4).

I can do the second part using the quotient rule. Does that answer the question?

Thanks :smile:

Reply 1

Killjoy-

You have to use the chain rule for the second part since it is a function within a function.

dy/dx = du/dx x dy/du

du/dx is your result.

(edited 12 years ago)

Reply 2

thegold94

I thought about that, but then where does dy/du come from?

Reply 3

Killjoy-

Original post by thegold94

I thought about that, but then where does dy/du come from?

Well, (x+1)/(x-1) is u.
So you can substitute this into the second equation they give you and you will see what I mean.

Reply 4

thegold94

I think I've got it. If u= (1+x)/(1-x), then I think I take y=u^3, differentiate that to dy/du = 3u^2, stick u in there and then end up multiplying 3(1+x)^2 / (1-x)^2 to get 6(1+x)^2 / (1-x)^4. That actually works. Thanks :smile:

Reply 5

Killjoy-